1. Field of the Invention
The invention relates to a multilayer wiring board and a manufacturing method for the multilayer wiring board.
2. Description of Related Art
In commonly-used multilayer wiring boards, a pattern of traces is formed by applying etching to copper foil bonded to a resin board. However, such multilayer wiring boards are not suitable for use under high current conditions, because the thickness of copper foil used in the multilayer wiring boards is limited.
Japanese Patent Application Publication No. 2013-211349 (JP 2013-211349 A) describes a multilayer wiring board in which a pattern of traces is provided by forming grooves on a resin board and filling the grooves with conductive paste. In this multilayer wiring board, it is possible to form a thicker wiring layer by increasing the depth of each groove. Thus, the multilayer wiring board described in JP 2013-211349 A is more suitable for use under high current conditions than the aforementioned commonly-used multilayer wiring boards. Electric currents, which are higher than electric currents to be applied to commonly-used home electric appliances, need to be applied to in-vehicle multilayer wiring boards. Therefore, there have been demands for in-vehicle multilayer wiring boards having a thicker wiring layer.
According to the technique described in JP 2013-211349 A, a plurality of thermoplastic resin boards, in which traces are formed in the grooves, is heated to a temperature equal to or higher than the softening temperature thereof, and thus the thermoplastic resin boards are bonded together under pressure. In other words, during the thermocompression bonding, the thermoplastic resin boards are entirely softened. This causes a possibility that the grooves will be deformed and thus the traces will fail to obtain desired electrical characteristics.